Methane conversion process

ABSTRACT

In an improved method for converting methane to at least one higher hydrocarbon product and coproduct water which comprises contacting a gas comprising methane and at least one added gaseous oxidant with nonacidic solid, the improvement comprising conducting at least a portion of said contacting in the presence of added water.

BACKGROUND OF THE INVENTION

This invention relates to the conversion of methane to higherhydrocarbons. A particular application of this invention is a method forconverting natural gas to more readily transportable material.

Recently, it has been discovered that methane may be converted to higherhydrocarbons by a process which comprises contacting methane and anoxidative synthesizing agent at synthesizing conditions (e.g., at atemperature selected within the range from about 500° to about 1000° C.)Oxidative synthesizing agents are compositions having as a principalcomponent at least one oxide of at least one metal which compositionsproduce C₂ + hydrocarbon products, co-product water, and a compositioncomprising a reduced metal oxide when contacted with methane atsynthesizing conditions. Reducible oxides of several metals have beenidentified which are capable of converting methane to higherhydrocarbons. In particular, oxides of manganese, tin, indium,germanium, lead, antimony, bismuth, praseodymium, terbium, cerium, ironand ruthenium are most useful. See commonly-assigned U.S. Pat. Nos.4,443,669 (Mn); 4,444,984 (Sn); 4,445,648 (In); 4,443,665 (Ge);4,443,674 (Pb); 4,443,646 (Bi); 4,499,323 (Pr); 4,499,324 (Ce); and4,593,139 (Ru), the entire contents of which are incorporated herein byreference. See also commonly-assigned U.S. patent application Ser. No.666,694 (Fe) the entire content of which is incorporated herein byreference.

Commonly-assigned U.S. Pat. No. 4,554,395 discloses and claims a processwhich comprises contacting methane with an oxidative synthesizing agentunder elevated pressure (2-100 atmospheres) to produce greater mounts ofC₃ + hydrocarbon products

Commonly-assigned U.S. Pat. No. 4,560,821 discloses and claims a processfor the conversion of methane to higher hydrocarbons which comprisescontacting methane with particles comprising an oxidative synthesizingagent which particles recirculate between two physically separatezones--a methane contact zone and an oxygen contact zone.

U.S. Pat. No. 4,499,322 discloses and claims a process for theconversion of methane to higher hydrocarbon and comprises contactingmethane with an oxidative synthesizing agent containing a promotingmount of alkali metal and/or compounds thereof.

U.S. Pat. No. 4,495,374 discloses and claims a process for theconversion of methane to higher hydrocarbons which comprises contactingmethane with an oxidative synthesizing agent containing a promotingamount of alkaline earth metal and/or compounds thereof.

Hinsen and Baerns report studies of a continuous mode for the oxidativecoupling of methane wherein regeneration air is cofed with methane feed.Hinsen, W. and Baerns, M., "Oxidative Koppling von Methan zu C₂ -Kohienwasserstoffen in Gegenwart untersehiedlicher Katalsatoren",Chemiker-Zeitung, Vol. 107, No. 718, pp. 223-226 (1983). Using acatalyst based on lead oxide and gamma-alumina in a fixed bed reactoroperated at 1 atmosphere total pressure and 600-750 degrees C., theyreport results of approximately 53% selectivity to ethane and ethyleneat 8% methane conversion for a feed consisting of about 50% methane, 25%air and 25% nitrogen. Other metal oxides studies by Hinsen and Baernsincluded oxides of Bi, Sb, Sn and Mn.

U.S. Pat. No. 4,523,049, discloses and claims a process for convertingmethane to higher hydrocarbons which comprises contacting methane and anoxygen-containing gas with a solid comprising a reducible metal oxideand an alkali/alkaline earth metal promoter.

U.S. Pat. No. 4,523,050 discloses and claims a process for convertingmethane to higher hydrocarbons which comprises contacting methane and anoxygen-containing gas with a manganese silicate.

Commonly-assigned U.S. patent application Ser. No. 738,110, filed May24, 1985, discloses and claims a method for converting methane to higherhydrocarbons wherein methane and a gaseous oxidant are contacted with anonacidic solid. In a preferred embodiment, the solid comprises analkali metal component associated with a support material. Theapplication also teaches conducting the contacting in the presence ofhalogen promoters when employing alk.ali-promoted solids..

Commonly-assigned U.S. patent application Ser. No. 738,114, filed May24, 1985, discloses and claims a process wherein methane and a gaseousoxidant are contacted with a nonacidic solid in the presence of halogenpromoter but in the absence of an alkali metal promoter.

Concurrently-filed, commonly-assigned U.S. patent application Ser. No.07/014,406 filed 2-13-87 discloses and claims a method for convertingmethane to higher hydrocarbons wherein methane and added water arecontacted in the substantial absence of added gaseous oxidant with asolid comprising at least one reducible metal oxide.

The reaction product of the foregoing processes are hydrocarbons, carbonoxides, coke and water. It would be beneficial in these processes toreduce selectivities to carbon oxides and coke and to increase methaneconversions to the desired hydrocarbon products. Accordingly, an objectof this invention is to provide an improved process for convertingmethane to higher hydrocarbons. More particular aspects, objects and theseveral advantages of this invention will become apparent to thoseskilled in the an upon reading this disclosure and the appended claims.

SUMMARY OF THE INVENTION

It has been found that processes for producing higher hydrocarbonswherein methane and a gaseous oxidant are contacted with a nonacidicsolid are improved when the contacting is conducted in the presence ofadded water. This added water is separate and apart from the coproductwater produced from methane conversion during the contacting. However,such coproduct water (or a portion thereof) may be separated from theother products and introduced into the contacting zone as the addedwater.

In processes conducted according to this invention, methane is convertedto higher hydrocarbons with improved efficiency, e.g., increasedselectivity to higher hydrocarbon products.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are plots respectively of the effect of steam partialpressure vs C₂ + hydrocarbon selectivity and steam partial pressure vs.CO_(x) formation rate from the tests described in Example 7.

DETAILED DESCRIPTION OF THE INVENTION

In addition to methane the methane feedstock, employed in the method ofthis invention may contain other hydrocarbon or non-hydrocarboncomponents. The methane content of the hydrocarbon portion of thefeedstock however, will typically be within the range of about 40 to 100vol. %, preferably within the range of about 80 to 100 vol. %, morepreferably within the range of about 90 to 100 vol. %.

The gaseous oxidant cofed with methane to the contacting zone preferablycomprises a gas containing molecular oxygen (e.g., air). However, oxidesof nitrogen, esp. N₂ O, have also been found to be effective gaseousoxidants. See U.S. Pat. No. 4,547,610, the entire content of which isincorporated herein by reference.

The ratio of hydrocarbon feedstock to oxygen-containing gas is notnarrowly critical to the present invention. Generally, it is desirableto control the hydrocarbon/oxygen molar ratio to avoid the formation ofgaseous mixtures within the flammable region. Preferably, the ratio ismaintained within the range of about 0.1-300:1, more preferably withinthe range of about 1-150:1. Methane/air feed mixtures containing about30 to 90 volume % methane have been found to comprise a desirablefeedstream. Further dilution of the feedstream with gases such asnitrogen may be beneficial for improved temperature control.

The amount of added water present during at least a portion of themethane/solid contacting may vary over a wide range. Preferably, themole ratio of added water to methane in the gas to be contacted is lessthan about 10. More preferably, this mole ratio is in the range of about0.01 to about 6, still more preferably about 0.05 to about 4.0. Theadded water may be combined with the methane-containing gas and/or theoxygen-containing gas prior to the contacting the nonacidic solid. Forexample, the methane-containing gas or the oxygen-containing gas may becontacted with water so that the gas "picks-up" a predetermined,controlled amount of added water prior to the methane/solid contacting.Alternately, a predetermined, controlled amount of water e.g., steam,can be injected into the methane-containing gas and/or theoxygen-containing gas and/or directly into the methane/solid contactingzone or zones.

The solids useful in the present invention are characterized as"nonacidic". This descriptor is meant to refer to the main, predominantsurface properties of the non-acidic solids. For example some solidbases are known to have acidic properties to some extent. See Tanabe,K., "Solid Acid and Base Catalysts."In: Catalysis Science & Technology,vol. 2 (New York, Springer-Verlag Berlin Heidelberg, 1981). Currentlypreferred nonacidic solids used in the present process are characterizedby negligible acidity (less than about 0.01 meg/gm) in the H_(o) rangeless than about 3.3, preferably less than about 6.8, H_(o) is theHaminert acidity parameter described on pp. 234-241 of Tanable.

A further characteristic of preferred nonacidic solids for the presentprocess is a relatively low surface area. Nonacidic solids havingsurface areas less than about 50 cm² /gm are suitable, but the surfaceareas of preferred solids are within the range of about 0.1-10 m² /gm.

In one distinct embodiment of this invention, methane and a gaseousoxidant are contacted with a nonacidic solid characterized by thesubstantial absence of reducible metal oxides. Characteristics ofnonacidic acids preferred for this embodiment are that they be stableand substantially nonreducible under process conditions. Examples ofsuitable nonacidic solids include those solid bases described in Table 2on p. 233 of Tanabe. supra. However, presently preferred nonacidicsolids are metal oxides and mixed oxides. Alkaline earth oxides areparticularly preferred, especially MgO and CaO. Other suitable metaloxides are SiO₂, alpha-Al₂ O₃, La₂ O₃, ThO₂, TiO₂, and ZrO₂. Suchmaterials are relatively stable under the conditions of the presentprocess.

Alkali metal-promoted alkaline earth oxides are preferred nonacidicsolids for this embodiment. Such solids are described and exemplified incommonly-assigned U.S. patent application Ser. No. 738,110, filed May24, 1985, the entire content of which is incorporated herein byreference. Halogen promoters may be employed, but in such event, the useof alkali metal promoters is not preferred. See commonly-assigned U.S.patent application Ser. No. 738,114, filed May 24, 1985, the entirecontent of which is incorporated herein by reference.

In another distinct embodiment of this invention, methane and a gaseousoxidant are contacted with solid comprising a reducible metal oxide.While such solids are sometimes referred to as "catalysts" it will beunderstood that, under conditions of use, nonacidic solids comprising areducible metal oxide act as selective oxidants, and, therefore, take onthe characteristics of a reactant during use. Thus, for example, theterm "Mn-containing oxides" is meant to embrace both reducible oxides ofMn and reduced oxides of Mn, it being understood reducible oxidescomprise the principal active component of the compositions.

In their active state, such catalysts comprise at lease one reducibleoxide of at least one metal, which oxide when contacted with methane atsynthesizing conditions (e.g., at a temperature within the range ofabout 500° to 1000° C.) produces higher hydrocarbon products, coproductwater, and a reduced metal oxide. The term "reducible" is used toidentify those oxides of metals which are reduced under the aforesaidconditions. The term "reducible oxides of metals" includes: (1)compounds described by the general formula M_(x) O_(y) wherein M is ametal and x and y designate the relative atomic proportions of metal andoxygen in the composition and/or (2) one or more oxygen-containing metalcompounds (i.e., compounds containing elements in addition to the metaland O), provided that such oxides and compounds have the capability ofproducing higher hydrocarbon products from methane as described herein.

Effective agents for the conversion of methane to higher hydrocarbonshave previously been found to comprise reducible oxides of metalsselected from the group consisting of manganese, tin, indium, germanium,antimony, lead, bismuth and mixtures thereof. See U.S. Pat. Nos.4,443,649; 4,444,984; 4,443,648; 4,443,645; 4,443,647; 4,443,644; and4,443,646. Reducible oxides of manganese are particularly preferredcatalyst components.

Reducible oxides of cerium, praseodymium, and terbium have also beenfound to be effective for the conversion of methane to higherhydrocarbons, particularly associated with an alkali metal componentand/or an alkaline earth metal component. See U.S. Pat. Nos. 4,499,324(Ce) and 4,499,323 (Pt) and also see commonly-assigned U.S. patentapplication Set. No. 06/600,918 (Tb).

Reducible oxides of iron and ruthenium are also effective, particularlywhen associated with an alkali or alkaline earth component. Seecommonly-assigned U.S. patent application Ser. No. 06/600,730 (Fe) andU.S. Pat. Nos. 4,489,215 and 4,593,139 (Ru).

Alkali and alkaline earth metals and compounds thereof have been foundto improve the hydrocarbon product selectivity of reducible metaloxides. The further incorporation of phosphorus into solids promoted byalkali or alkaline earth components enhances catalyst stability. Seecommonly-assigned U.S. Pat. Nos. 4,499,322 and 4,495,374, the entirecontent of which are incorporated herein by reference. Alkali metals areselected from the group consisting of lithium, sodium, potassium,rubidium and cesium. Lithium, sodium and potassium, and especiallylithium and sodium, are preferred alkali metals. Alkaline earth metalsare selected from the group consisting of magnesium, calcium, strontiumand barium. Presently preferred members of this group are magnesium andcalcium. Compositions derived from magnesia have been found to beparticularly effective catalytic materials. Boron and compounds thereofare also desirably present in the reducible metal oxide catalystemployed in the process of this invention. See commonly-assigned U.S.patent application Ser. No. 06/877,574, entire content of which isincorporated herein by reference. One class of boron-promotedcompositions useful in the process of this invention comprises:

(1) at least one reducible metal oxide,

(2) at least one member of the group consisting of boron and compoundsthereof, and

(3) at least one member of the group consisting of oxides of alkalineearth metals.

A related class of catalyst compositions further comprises at least onealkali metal or compound thereof. Sodium and lithium are preferredalkali metal components.

One further, special class of catalyst compositions useful in theprocess of this invention are mixed oxides of sodium, magnesium,manganese and boron characterized by the presence of the crystallinecompound NaB₂ Mg₄ Mn₂ O_(x) wherein x is the number of oxygen atomsrequired by the valence states of the other elements, said compoundhaving a distinguishing x-ray diffraction pattern. In its most activeform, the compound is believed to correspond to the formula NaB₂ Mg₄ Mn₂O₁₁. While this crystalline compound has been found to be associatedwith highly effective oxidant compositions, it has further been foundthat still better results are obtained when the oxidant is characterizedby both: (1) the presence of crystalline compound NaB₂ Mg₄ Mn₂ O_(x) and(2) a stoichiometric excess of of Mn relative to at least one of theother elements of the crystalline compound. In currently preferredoxidants of this type, a stoichiometric excess of Mn relative to B isprovided. In a still more specific preferred embodiment excess amountsof Na and Mg, as well as Mn, are present in the mixed oxide compositionrelative to the amounts required by the amount of boron present tosatisfy the stoichiometry of the compound NaB₂ Mg₄ Mn₂ O_(x).

Further examples of components which may be present in the catalystsused in the process of this invention are halogen and chalcogencomponents. Such components may be added either during preparation ofthe catalysts or during use. Methane conversion processes employinghalogen-promoted reducible metal oxides are disclosed in U.S. Pat. No.1,544,784. Methane conversion processes employing chalcogen-promoted,reducible metal oxides are disclosed in U.S. Pat. No. 4,544,785.

The reducible metal oxides compositions may be supported by or dilutedwith support materials such as silica, alumina, titania, zirconia andthe like, and combinations thereof. When supports are employed, alkalineearth oxides, especially magnesia, are preferred.

The catalysts are conveniently prepared by any of the methods associatedwith similar compositions known in the art. Thus, such methods asprecipitation, co-precipitation, impregnating, granulation, spray dryingor dry-mixing can be used. Supported solids may be prepared by methodssuch as adsorption, impregnation, precipitation co-precipitation, anddry-mixing. For example, compounds of Mn,Sn,In,Ge,Pb,Sb,Bi,Pr,Tb,Ce,Feand or Ru may be combined with compounds of other components in anysuitable way. Substantially any compound of the components can beemployed. Compounds typically used would be oxides or organic orinorganic salts of the recited components.

To illustrate, when preparing a catalyst containing: (1) a reduciblemetal oxide component (e.g., Mn). (2) an alkali metal component, (3) aboron component and (4) an alkaline earth component; one suitable methodof preparation is to impregnate compounds of the fourth component of thecomposition with solutions of compounds of Mn, alkali metals, and/orboron. Suitable compounds for impregnation include the acetates, acetylacetonates, oxides, carbides, carbonates, hydroxides, formates,oxalates, nitrates, phosphates, sulfates, sulfides, tartrates,fluorides, chlorides, bromides, or iodides. After impregnation thepreparation is dried to remove solvent and the dried solid is calcinedat a temperature selected within the range of about 300° to 1200° C.Particular calcination temperatures will vary depending on the compoundsemployed. Preferably, the alkaline earth component is provided as theoxide. Preferably, the alkali metal component is provided as a basiccomposition of the alkali metal(s). Examples are sodium hydroxide,sodium acetate, lithium hydroxide, lithium acetate, etc. When P isemployed as an additive, it has been found desirable to add the alkalimetal and P to the composition as compounds such as the orthophosphates,metaphosphates, and pyrophosphates of alkali metals. Pyrophosphates arepreferred. Sodium pyrophosphate is particularly preferred. Preferably,the boron component is provided as boric acid, boric oxide (oranhydride), alkali metal borates, boranes, borohydrides, etc.,especially boric acid or oxide.

Formation of the crystalline compound NaB₂ Mg₄ Mn₂ O_(x) may beaccomplished by reacting active compounds of the substituent elements. Asuitable mixture of the reactive compounds is formed and heated for atime sufficient to form the crystalline material. Typically, atemperature of about 850° to about 950° C. is sufficient. When preparingmixed oxide compositions characterized by the presence of othercrystalline compound, the composition is desirably incorporated withbinders or matrix materials such as silica, alumina, titania, zirconia,magnesia and the like.

Regardless of which particular catalyst is prepared or how thecomponents are combined, the resulting composite will generally be driedand calcined at elevated temperatures prior to use. Calcination can bedone under air, H₂, carbon oxides, steam, and/or inert gases such as N₂and the noble gases.

Preferably, methane is contacted with reducible metal oxides in thepresence of added water and in the substantial absence of catalyticallyeffective nickel, noble metals and compounds thereof, (i.e., nickel,rhodium, palladium, silver, osmium, iridium, platinum and gold) tominimize the deleterious catalytic effects thereof. These metals, whencontacted with methane at the temperatures employed in the methanecontacting step of the present invention, tend to promote cokeformation, and the metal oxides tend to promote the formation ofcombustion products rather than the desired hydrocarbons. The term"catalytically effective" is used herein to identify the quantity of oneor more of nickel and the noble metals and compounds thereof whichsubstantially changes the distribution of products obtained in themethod of this invention relative to such contacting in the absence ofsuch metals and compounds thereof.

Regardless of which class of contacting solid is selected (i.e.,reducible or nonreducible solid), operating temperatures are generallywithin the range of about 300° to about 1200° C.

If nonacidic solids are employed without the presence of reducible metaloxides, operating temperature are preferably within the range of about700° to about 1200° C., more preferably about 800° to about 1000° C.

If reducible metal oxides are employed, the temperature selected maydepend in part on the particular reducible metal oxide(s) employed. Bestresults for contact solids containing manganese have been found atoperating temperatures within the range of about 800 degrees to 900degrees C. Reducible oxides of certain metals may require operatingtemperatures below the upper part of the recited range to minimizesublimation or volatilization of the metals (or compounds thereof) durinmethane contact. Examples are: (1) reducible oxides of indium,(operating temperatures will preferably not exceed about 850° C.); (2)reducible oxides of germanium (operating temperatures will preferablynot exceed about 850° C.); and (3) reducible oxides of bismuth(operating temperatures will preferably not exceed about 800° C.).

Operating pressures are not critical to the presently claimed invention.However, both general syste pressure and partial pressures of methaneand water have have been found to effect overall results. Preferredgeneral system pressures are within the range of about 0. 1 to 30atmospheres.

The space velocity of the gaseous reaction streams are similarly notcritical to the presently claimed invention, but have been found toeffect overall results. Preferred total gas hourly space velocities arwithin the range of about 100 to 300,000 hr.⁻¹, more preferably withinthe range of about 600 to 100,000 hr.⁻¹.

Contacting methane and a reducible metal oxide to form higherhydrocarbons from methane also produces coproduct water and reduces themetal oxide. The exact nature of the reduced metal oxides are unknown,and so are referred to as "reduced metal oxides". Regeneration ofreducible metal oxides in the method of the present invention occurs "insitu"-by contact of the reduced metal oxide with the oxygen cofed withmethane to the contact zone.

The solids may be maintained in the contact zone as fixed, moving, orfluidized beds of solids. A fixed bed of contact solids is currentlypreferred for the method of this invention.

The effluent from the contact zone contains higher hydrocarbon products(e.g., ethylene, ethane and other lighter hydrocarbons), carbon oxides,water and unreacted hydrocarbons (e.g., methane). Higher hydrocarbonsmay be recovered from the effluent and, if desired, subjected to furtherprocessing using techniques known to those skilled in the art. Unreactedmethane may be recovered and recycled to the contact zone.

The invention is further illustrated by reference to the followingexamples.

COMPARATIVE EXAMPLE A AND EXAMPLES 1-2

A gaseous feedstream of air/methane and, in Example 1 steam, wascontacted with solid MgO (suppied by Kaiser Chemicals) which wasimpregnated with lithium to contain 0.36% by weight of lithium,calculated as elemental metal. Results are shown in Table I.

                  TABLE I                                                         ______________________________________                                                    Comparative        Example                                                    Example A                                                                              Example 1 2*                                             ______________________________________                                        Temperature, °C.                                                                     909        884       897                                        Methane GHSV hr..sup.-1                                                                     23,700     25,000    25,000                                     Total Pressure, Psia                                                                        19.7       34.7      19.7                                       O.sub.2 Partial Pressure, Psi                                                               0.55       0.52      0.52                                       CH.sub.4 Partial Pressure, Psi                                                              7.56       7.97      7.96                                       H.sub.2 O Partial Pressure, Psi                                                             0          15.0      0                                          CH.sub.4 Conversion, %                                                                      1.44       10.1      3.76                                       O.sub.2 Conversion, %                                                                       8.36       58.0      21.3                                       C.sub.2 + Selectivity, %                                                                    86.9       93.5      91.5                                       ______________________________________                                         *Note: Steam was excluded from the feed to the contacting zone for 45         minutes before the Example 2 sample was collected.                       

These Examples were run one after the other in the order shown.

These results demonstrate certain of the substantial benefits of thepresent invention. For example, the presence of water during thecontacting provides for increased methane conversion, oxygen conversionand selectivity to the valuable C₂ + hydrocarbons. In addition,comparing Example 2 to Example 1 and Comparative Example A suggests thatcertain of the beneficial effects of added water may last after wateraddition is complete. Thus, it is possible to obtain at least a portionof the benefits of water addition by periodic, rather than continuous,addition of water.

EXAMPLES 3-6 and COMPARATIVE EXAMPLES B-C

A contact solid consisting of 15% by weight manganese (calculated aselemental metal) and 5% by weight Na₄ P₂ O₇ on silica was prepared byimpregnating the silica support with appropriate amounts of sodiumpyrophosphate and manganese (as manganese acetate). The impregnatedsolid was dried and then calcined in air.

A quartz tube reactor was charged with the calcined solids. A series ofexperiments were run at one atmosphere total pressure using a gaseousmixture of 10% by volume of air in methane to contact these calcinedsolids. When steam was added it equaled 14% of the total number of molesof methane and air fed to the reactor

Results are shown in Table II.

                  TABLE II                                                        ______________________________________                                               EXAMPLE                                                                       B     C       3       4     5     6                                    ______________________________________                                        Temperature,                                                                           900     900     900   899   900   900                                °C.                                                                    CH.sub.4 GHSV,                                                                         15000   15000   15000 15000 15000 15000                              hr..sup.-1                                                                    Steam Added                                                                            No      No      Yes   Yes   Yes   Yes                                CH.sub.4 Conver-                                                                       2.8     2.7     3.5   3.1   3.1   3.7                                sion, %                                                                       O.sub.2 Conver-                                                                        83.5    81.6    --    68.6  66.9  74.2                               sion, %                                                                       C.sub.2 = Selec-                                                                       21.9    20.3    30.6  28.4  29.3  33.5                               tivity, %                                                                     C.sub.2 Selec-                                                                         40.1    40.4    44.7  43.8  46.6  40.5                               tivity, %                                                                     C.sub.3 Selec-                                                                         1.6     1.4     2.6   2.7   2.2   3.7                                tivity, %                                                                     >C.sub.4 Selec-                                                                        0       0       0.2   0.2   0     0.3                                tivity, %                                                                     C.sub.2 + Selec-                                                                       63.7    62.0    78.1  75.1  78.1  77.9                               tivity, %                                                                     ______________________________________                                    

These results demonstrate certain of the benefits of the presentinvention. For example, the presence of steam during themethane/air/contact solids contacting does provide for generally highselectivity to valuable C₂ + hydrocarbons.

EXAMPLE 7

A series of runs were made using the Li/MgO described in ComparativeExample A and Examples 1-2. Partial pressure of methane ranged fromabout 7.5 to 8.0 psia and that of oxygen from about 0.5 to 0.62 psia.Partial pressure of steam ranged from about 0.5 to 15 psia. Methane GHSVranged from about 23,700 to 25,000 hr.⁻¹ and temperature from about 884°to 909° C.

The results achieved are depicted graphically in attached FIGS. 1 and 2.Referring to FIG. 1, it can be seen that the addition of steam to thefeed mixture has a substantial effect on the selectivity of the reactionto the desired C₂ ⁺ hydrocarbon products.

As shown in FIG. 2, the reaction rate is increased by a very significantextent by the addition of steam to the feed.

While this invention has been described with respect to various specificexamples and embodiments, it is to be understood that the invention isnot limited thereto and that it can be variously practiced within thescope of the following claims.

What is claimed:
 1. In a method for converting methane to higherhydrocarbons wherein a gas comprising methane and a gaseous oxidant arecontacted with a nonacidic solid .Iadd.which is substantiallynonreducible under the contacting conditions .Iaddend.to produce higherhydrocarbons and coproduct water, the improvement which comprisesconducting at least a portion of said contacting in the presence ofadded water. . .2. The method of claim 1 wherein said solid comprises atleast one reducible metal oxide of at least one metal..!.3. The methodof claim 1 wherein the mole ratio of said added water to said methane insaid gas is less than about
 10. 4. The method of claim 1 wherein themole ratio of said added water to said methane in said gas is in therange of about 0.01 to about
 6. 5. The method of claim 1 wherein themole ratio of said added water to said methane in said gas is in therange of about 0.05 to about 4.0.
 6. The method of claim 1 wherein thecontacting is conducted at a temperature within the range of about 300°to about 1200° C.
 7. The method of claim wherein the contacting isconducted at a temperature of about 700° to about 1200° C.
 8. The methodof claim 1 wherein the contacting is conducted at a temperature of about800° to about 1000° C.
 9. The method of claim 3 wherein the contactingis conducted at a temperature of about 500° to about 1000° C.
 10. Themethod of claim 1 wherein said solid is selected from the groupconsisting of basic metal oxides.
 11. The method of claim 10 whereinsaid solid is selected from the group consisting of alkaline earthoxides and mixtures thereof.
 12. The method of claim 10 wherein saidsolid comprises magnesia.
 13. The method of claim 10 wherein said solidcomprises CaO. The method of claim . .10.!. .Iadd.1 .Iaddend.whereinsaid solid comprises titania.
 15. The method of claim . .10.!. .Iadd.1.Iaddend.wherein said solid comprises silica.
 16. The method of claim 10wherein said solid comprises barium. . .17. The method of claim 2wherein said solid is substantially nonreducible under the contactingconditions..!.18. The method of claim . .11.!. .Iadd.1 .Iaddend.whereinsaid solid . .further.!. comprises .Iadd.an alkaline earth oxidetogether with .Iaddend.at least one alkali metal component.
 19. Themethod of claim 18 wherein the alkali metal component is selected fromthe group consisting of sodium and compounds thereof.
 20. The method ofclaim 18 wherein the alkali metal component is selected from the groupconsisting of lithium and compounds thereof.
 21. The method of claim 18whereto the alkali metal component is selected from the group consistingof potassium and compounds thereof.
 22. The method of claim 1 whereinthe gaseous oxidant comprises molecular oxygen.
 23. The method of claim1 wherein the gaseous oxidant comprises oxides of nitrogen.
 24. Themethod of claim 23 wherein the oxides of nitrogen comprises N₂ O. . .25.In a method for converting methane into higher hydrocarbon products andcoproduct water which comprises contacting a gas comprising methane andan oxygen-containing gas with a solid comprising at least one reduciblemetal oxide of at least one metal, which oxide when contacted withmethane at 500° to 1000° C. produces higher hydrocarbons, coproductwater, and reduced metal oxide, the improvement comprising conducting atleast a portion of the contacting in the presence of added water..!...26. The method of claim 25 wherein the mole ratio of said added waterto said methane in said gas is less than about 10..!.. .27. The methodof claim 25 wherein the mole ratio of said added water to said methanein said gas is in the range of about 0.01 to about 6..!.. .28. Themethod of claim 25 wherein the mole ratio of said added water to saidmethane in said gas is in the range of about 0.05 to about 4.0..!.. .29.The method of claim 25 wherein the solid comprises at least on reducibleoxide of Mn..!.. .30. The method of claim 29 wherein the solid comprisesat least one member of the group consisting of alkali metals, alkalineearth metals, and compounds and mixtures thereof..!.. .31. The method ofclaim 29 wherein the solid comprises at least one member of the groupconsisting of boron and compounds thereof..!.. .32. The method of claim30 wherein the solid comprises at least one member of the groupconsisting of boron and compounds thereof..!..Iadd.33. A method for theoxidative conversion of methane to higher hydrocarbons and coproductwater, comprising: contacting said methane, a free oxygen-containing gasand water with at least one solid contact material which issubstantially nonreducible under the contacting conditions selected fromthe group consisting of a solid contact material consisting essentiallyof lanthanum oxide and solid contact materials comprising (a) at leastone promoter comprising an alkali metal and (b) at least one basematerial selected from the group consisting of magnesium oxide andcalcium oxide, under oxidative conversion conditions sufficient toconvert said methane to said higher hydrocarbons. .Iaddend..Iadd.34. Aprocess in accordance with claim 33, wherein said solid contact materialconsists essentially of at least one lithium-containing promoter andmagnesium oxide as base material. .Iaddend.